1. Field of the Invention
The field of the present invention is woven fabrics of synthetic yarns as may be used in papermaking and other industrial processes.
With the advent of flat woven papermakers fabrics, the need to join or seam the fabric into an endless belt became a major concern in the production of papermaker's fabrics. Many seams such as the coil seam were developed to join the fabric ends. With the increased speed, heat, and chemical deterioration associated with the use of newer papermaking equipment and higher production temperatures, the prior art coil seam materials and joining wires are proving insufficient to meet the demands of the industry.
2. Description of the Prior Art
Originally papermaking fabrics were woven endless and were placed on the machine as a single fabric without the need for seaming or any other method of joining the ends. However, over time, as the papermaking equipment grew in size and the fabrics grew in response thereto, it became desirable to weave the fabrics in what is known as a flat woven condition and to join the fabrics into an endless belt by means of seaming the fabrics. Over the years many methods have been developed to take flat woven fabrics and join them into an endless belt.
One early attempt at joining the fabrics was the use of lacing methods which entailed great work and difficulty in addition to producing seams of questionable reliability. Such a method is exemplified in U.S. Pat. No. 340,335.
Another prior art method for joining together flat woven belts in order to make them continuous is shown in U.S. Pat. No. 1,841,303. In this method a plurality of metallic elements were secured onto each end of the fabric to form a plurality of loops which were then interlaced and joined by a single pintle or hinge wire. Over the years this method was developed and refined and was frequently referred to in the industry as a clipper hook seam.
Another method for joining flat woven felts into an endless unit was through the use of a zipper or closure member. Such a method is disclosed in U.S. Pat. No. 1,852,732 and U.S. Pat. No. 1,948,411 and U.S. Pat. No. 1,986,785.
Another method of doing this is what is known in the art as the Pintle seam which is exemplified by U.S. Pat. No. 2,629,909.
Another prior art attempt to join the flat woven fabric into an endless belt was the use of interwoven formed warps which are formed and rewoven into the fabric to produce a plurality of loops through which the joining wire may be located. One example of this technique is U.S. Pat. No. 2,883,734.
Another prior art attempt at joining the belts was comprised of folded over end portions which were stitched to form loops which were interlaced and through which a flat key or joining means could be located. An example of this construction is U.S. Pat. No. 3,309,790.
Additional attempts to join the ends of fabric belts are shown in U.S. Pat. Nos. 3,316,599, 3,324,516, 3,335,844, 3,581,348, 3,664,907, 4,006,760, 4,026,331, 3,281,905, and 4,250,882.
With reference to U.S. Pat. No. 4,250,882, entitled LOW BULK PIN TYPE SEAM FOR USE IN PAPERMAKER'S EQUIPMENT FABRICS SUCH AS DRYER FELTS, the pin seam construction set forth therein is one which is compatible with the use of the joining wire and coil material in accordance with the instant invention. Additionally, U.S. Pat. No. 4,351,049, entitled STITCHLESS LOW BULK PIN TYPE SEAM FOR USE IN PAPERMAKING EQUIPMENT FABRICS, SUCH AS DRYER FELTS also sets forth a procedure which is compatible with the instant invention.
While most of the prior art constructions for joining fabric ends have proven successful as to the methodology employed, many of the fabric seams have been unsatisfactory because of the materials used in forming the seam. For instance, difficulty has been experienced with the metallic hooks used in making the fabric seam in addition to the associated problems which arise from the wear generated by the metallic members. Likewise, those seams which have attempted to employ yarns or strands actually taken from the body of the fabric and back woven thereto have met with limited success due to the stresses put on the materials. In addition, many of the prior art constructions which have employed independently constructed coils and joining wires have experienced difficulties due to the harsh environment in which the fabric must operate.
Woven fabrics fashioned into endless belts for conveying and guiding products under manufacture are used in various industrial processes. Both metallic and synthetic materials have been used for these flat woven belts as well as the seams joining the ends. As the industry and manufacturing equipment have advanced, the use of high speed and/or high temperature conditions have become more common. The more demanding conditions likewise are more destructive of the seam. Two synthetic materials which have found some use in high temperature applications are polymers known by the Trademarks Nomex and Kevlar, as reported in U.S. Pat. No. 4,159,618 and available from the Du Pont Company. These materials are twisted from multifilaments, or staple fibers into yarns, and are not available for applications where monofilament threads are preferred. Having a relatively rough, porous surface a multifilament can be difficult to keep clean in applications where contaminants are a problem. In addition to problems with contaminants, multifilaments often fail to retain their form or shape and can be difficult to join. For the foregoing reasons, Nomex and Kevlar yarns are sometimes coated with suitable resins to simulate monofilaments. These composite coated yarns can be used in fabrics where elevated temperatures are frequently encountered: however, under extended high temperature exposure, dry or moist, there can be a severe loss in tensile strength, as further reported in the above cited patent. An additional difficulty with composite yarns is that they do not withstand the physical abuse of abrasion during their operation.
Another synthetic material monofilament used with industrial conveying and guiding belts is polyester. It has gained widely accepted usage in the forming, press and dryer sections of papermaking machines because of its abrasion resistance, ability to flex, dimensional stability after being thermoset, chemical inertness, and ease of handling. Over the years techniques have been developed for weaving, thermosetting and seaming, polyester yarns and fabrics so that this material can be readily handled in the manufacture of endless belts. Polyester consequently enjoys wide acceptance; however, this material has poor high temperature hydrolytic stability, and cannot be satisfactorily used under moist conditions at continuous elevated temperatures. In papermaking applications, for example, it can be a limiting factor for the temperatures under which drying procsses can be carried out, and where high temperatures are desired some other material must be resorted to.
As can be seem from the above, the prior art has recognized that the currently available materials do not provide a seam of sufficient temperature, abrasion or hydrolysis resistance.